From time to time it would be useful to be able to limit searches to specific strings.  Such as, the ability to specify the string "xyz" and not have "abc...xyz" included in the results.

Yes; thanks for asking.
I'm giving you simple and simplified examples, because I frankly cannot remember the exact situations that prompted me to write with this suggestion. They come up regularly.  These are specific illustrative examples about the general problem -- not looking for a specific solutions to the examples.

Example 1:  For my work, I have hundreds of records with the word "Carbonite" in them.  Searching mSecure, it is not possible to find only the records with the specific word "car" or "carbon" in them.

Example 2: I've been using the internet for a long time and have many accounts with username based on a particular string; call it "ABC" and, e.g., "ABCPepper".  The "ABC" version recently showed up on a breached list and I wanted to try to isolate other accounts with that particular username string. But any search for just "ABC" in mSecure would also bring up every inclusive instance of that string.

Example 3: My mSecure database has many people's names in it.  If I want to find only, e.g., "Ann," I cannot without wading manually through, "Anne," "Anna," "Joann," "Maryanne," and you get the idea.  I want to be able to ask mSecure to show me only the records that contain (for this example) the specific string "Ann".  

Thanks again for asking.  The simple and common  double-quote delimiter to signal a specific string would be super!  That is: the string Ann would match any, but the quoted string "Ann" would only match that.

Yes; thanks for asking.
I'm giving you simple and simplified examples, because I frankly cannot remember the exact situations that prompted me to write with this suggestion. They come up regularly.  These are specific illustrative examples about the general problem -- not looking for a specific solutions to the examples.

Example 1:  For my work, I have hundreds of records with the word "Carbonite" in them.  Searching mSecure, it is not possible to find only the records with the specific word "car" or "carbon" in them.

Example 2: I've been using the internet for a long time and have many accounts with the usernames (something like this fake)  "ABC" and "ABCMike".  "ABC" recently showed up on a breached list and I wanted to try to isolate other accounts with that particular username, but could not successfully search for just those with mSecure.  

Example 3: My mSecure database many human names in it.  If I want to find only, e.g., "Ann," I cannot without wading manually through, "Anne," "Anna," "Joann," "Maryanne," and you get the idea.  I want to ask mSecure to just show me the "Ann" records.  

Thanks again for asking.  The simple and common  double-quote delimiter to signal a specific string would be super!  That is: the string Ann would match any, but the quoted string "Ann" would only match that.